The present invention generally relates to fluid displacement and pressurizing devices, and methods of assembling such devices.
More specifically, the present invention effectively relates to improvements over the devices and methods of assembly disclosed in U.S. Pat. Nos. 6,796,959; 6,938,319; 8,191,457 and 8,499,681, all of which are incorporated herein by reference in their entirety.
The devices disclosed in those patents utilize a carrier member (see, for example, part number 110 in the '959 and '319 patents) that is inserted longitudinally along the longitudinal axis of the bore of the syringe housing, and then is rotated to engage within the syringe housing and lock against further movement. While the devices disclosed in those patents are reliable for their intended purpose, because the devices are configured such that the carrier member must be longitudinally installed, and then must be rotated to lock the carrier member in place relative to the syringe housing (see, for example, part number 42 in the '959 and '319 patents), before the plunger thread engagement and release mechanism (i.e., the nut member 80 and link members 102, 104 in the '959 and '319 patents) can be installed, none of the devices lend themselves well to an automated method of assembly. Assembly steps to install the carrier member require a longitudinal introduction of the carrier member along the longitudinal axis of the syringe housing, followed by approximately a 90 degree or one-quarter turn rotation to seat and lock the carrier member in place. This installation process is described, for example, at col. 10, lines 3-9, of the '959 patent. This assembly method, which prevents installation of the plunger thread engagement and release mechanism (i.e., the nut member 80 and link members 102, 104 in the '959 and '319 patents) into the carrier member until after the carrier member is seated and locked in the syringe housing, slows the device assembly process.
There is an increasing demand in certain medical fields for disposable syringes made of plastic resin polymers for delivering a large volume of fluid at ultra-high pressure. Some new orthopedic applications, such as expanding inflatable orthopedic nails and bone cement delivery through small cannulas, can require pressures up to 2,700 p.s.i. These extreme pressures require that a user supply a great deal of plunger input torque. In some instances, the required input torque can be twice the force experienced in previous lower pressure applications, which therefore necessitates that the device being used include adequate handles to allow a user to comfortably hold and control the device during pressurization.
Compared to low pressure applications, ultra-high pressure applications present additional challenges when it comes to designs such as that which is disclosed in the previously-identified patents. For example, the extremely high frictional engagement of the heavily loaded nut member (see, for example, part number 80 in the '959 And '319 patents) against the carrier member (i.e., part number 110 in the '959 and '319 patents) combined with the nut member's rotational movement upon release has potential to reverse the quarter-turn rotation used to seat and lock the carrier member (i.e., relative to the syringe housing (i.e., part number 42 in the '959 and '319 patents)). These unlocking forces are transferred directly into the housing through the carrier's retaining mechanism (i.e., part number 172 in the '959 and '319 patents), thereby causing the housing to twist. In order to prevent being overcome by friction induced rotation during unlocking, this retaining mechanism must also be made much larger and more rigid. User input torque required to attain ultra-high pressures using prior art devices, such as that which is disclosed in the previously-identified patents, can also cause the device housing structures to twist in response to torsional loads applied during pressurization. Therefore, these prior art devices must not only have added structure to withstand very high longitudinal plunger loads associated with their pressure capability, but they must also have additional structure to resist torsional reaction from rotational plunger advancement and release of the nut member. Additionally, this high longitudinal loading which transfers directly from the nut member to the carrier member is distributed from the carrier member to the syringe housing by means of a symmetrical pair of bayonet style ears (i.e., part number 172 in the '959 And '319 patents) that, by their very nature (i.e., due to their configuration), can each never be made to engage the housing by more than a quarter of the carrier member's outside diameter. The engagement surface area for these ears is therefore limited, and operation under extreme pressure loading has been shown to exceed the compression strength of the polymers from which the housing and carrier member are formed.